Electronic grounding apparatus



Sept. 23,1952

R. A. RIDDLE ETAL ELECTRONIC GROUNDING APPARATUS 2 SHEETS-SHEET 1 Filed June 15, 1950 INVENTOR for A. Buwu: A/YD 27150170191. J MES/l BY M TTORN Ys Wm 3 Q M \Q Q Q 3 & b1 Q w {N (NP mutt out p 1952 R. A. RIDDLE ETAL 2,611,862

I ELECTRONIC GROUNDING APPARATUS Filed June 15, 1950 2 SHEETS--SHEET 2 INVENTOR Roy A. R1001: AND

Ramon: J Mas/1 BY ATTOR EYS Patented Sept. 23, 1952 UNITED STATES new "mm-E f ELECTRONIC .GROUNDING. APPARATUS Roy A. Riddlesummit'; N. v1., and Theodore J.

Mesh, E'asthampton, Mass;

"Pearl Kilpatrick Riddle, administratrix of .said Roy A. Riddle, deceased, and said- Theodore J. Mesh assignors to-Gilbert & Barker Manufacturing Company, West Springfield, Mass., a corporationnf Mas- .sachusetts Application June 15, 1950, srnrno. 168,282

More-particularly, the invention has for anobject theprovision of an'electrical operator for eifecting sig-nals or-any other work, and to control this "operator electronically; energizing it whenthe grounding cableis electrically connected'to-the tank of the truck, characterized in that the electrical capacity-of the tank with 'reference tothe-ground may be utilized to unbalance an electronic control circuit and-causethe operatorto-beenergized.

The --in-vention will lee-disclosed in connection with one illustrative example of it in the accompanyin'g drawings, in which: I

Fi-g;-1 isadiagram showing the apparatus and its electrical circuits;

2 5 aside elevational view' ofthehousingfonthe apparatus;

Fig; 3 is a top plan view of such" housing "as itappears with the cover removed; and

Fig.4 is afragmentarywiring diagr'amshowing 'a"modification in the form of "the electrical operator.

eferringyto'these drawings and first to the di-agrammatioal illustration of the invention in Eig. 1, it is desied to energize an electrical 'oper-' atorof any suitable and desired kind, whenever a grounding wireis properly connected to .the tank of a tank truck- This operator may, iorexample,

be usedto cause asignal, either visual :or audible,-

to foe-given or to control .a valve-in 'a pipe line used tosupplythertank with .oil, orin other ways. ,As herein illustrated, the operator :is shown: as a relay-- I, operable when I energized,'tor actuate a suitable switch, moving the blade-'32. into 1 engagement withvthe contact"3 .in this case. This switch may control any suitableelectrical circuit to perform the work desired. But the relay co'i'l may, when energized-cause the desired-workto be performed mechanically as well as electrically. Also, the

relayis not inah cases necessary although it is generally desirable because of the low-operating current available in the present apparatus;

In general, the relay I, or other electrical erator, is controlled by an electronic:tube;.:iin this casea tr'iode l, therelay'being in series with the'plate S' and cathode =6 ma circuit .supplied from a suitable source of electricity. ThetubeA isnor-mally i1on-conducting and 'the relayfil is not energized! Abridge circuit '1, 'to the input terminals tand- 9 of which is impressed-sa radio frequency voltage of low amplitude, hasrits outs. put terminals ill and II respectively connected to the grid 12 of tube--4 and-tothe grOund Normally; the impedances in the bridge circuit are balances and no voltage appears at the output terminals-m-andl l. The cableused to ground the tank of the truck; is indicated at 1 3. O ne' end of this cable is connected to theinputtermrnal 9 of the bridge circuit and through one :arm

of such circuitto the output terminal H of the bridge circuit and thus to the ground. The other end of cable I3 is adapted to beelectricallyconnected to the tank of 'thetruck. -When thecable is so connected, theelectrostatic capacity of the truck with reference to-the ground becomes con-- nected into one arm-0f the bridge -circuit,*un balancing the latter and causing =a-radio fre quency voltage to appear atth-e output terminals of the bridge circuit, and this causes the trlode 4'- to become conducting, whereby the relay l 15 energized.

Power for the apparatus may be securedfroma 115 volt, cycle, alternating current source, adapted to be connected to the terminals l l' an'd I5 The ungrounded terminal M'is connected by awire Hi 'to a half-wave rectifier l1,-which=maybeef the selenium cell type. This'rectifieris connected by a wire If! to one terminal of=-a current-limiting"resistor 19 of say 30-0hms resistance, and the other terminal of the-latteris connected by a wire 2t tothe terminal 2! one voltage divider, comprising a 10,000 ohrn'resistor 22 and a 1000 ohm variableresistor 23 connected inseries; The other terminal 24 ofthe' voltage divider is connected bya wire 25 to-power ter ml nal 15. The plate-cathode circuit oitriode 451s supplied'from theterminal 2! and the variable terminal 260i the voltage divider. A wire 21' con'- nects terminal zl to one end of relay coil I and the'otli'enend of the latteris connected rye wire" terminals 24 and -26.--'- The grid [2 is "connected I by a wire 3| to the output terminal I of the bridge circuit and the other output terminal II of the latter is connected by a wire 32 to wire 30. A condenser 33, say of .003 mfd. capacity, is connected across the wires 29 and 30 and provides a high frequency path from the cathode and wire 29 to wire 30 and the ground. The relay coil I may, for example, have a resistance of 5000 ohms. A condenser 34, of say .1 mid. capacity, is bridged across the relay coil I for the purpose of smoothing out the pulses of the voltage impressed on the relay.

The bridge circuit includes an inductance 35 in that arm which extends between the terminals 9 and II. This inductance may, for example, be a 10 millihenry, powdered iron core, radio frequency choke. It forms part of the connection from grounding cable I3 to the ground and provides a low impedance path for static electricity and a high impedance path for high frequency current. It enables the, radio frequency signal to be superposed on the grounding cable I3. A similar inductance 36 is provided in that arm of the bridge circuit which extends between the terminals 9 and III. A condenser 37, of say .001 mfd. capacity, is provided in that arm of the bridge circuit which extends between the terminals I0 and 8' and a similar condenser 38 is provided in the arm which extends between the terminals 3 and I- I.- The impedances and 36 and 37 and 38 are normally balanced and no voltage appears at output terminals I0 and II.

It is, deemed preferable to shield the grounding cable I 3 and a shield is conventionally shown at 39. This shield is grounded, as indicated. When the cable I3 is not connected to the tank truck, it forms with its shield a condenser which is bridged across the inductance 35. A condenser 40 of approximately the same capacity as that of cable I3 and shield 39, in this case .005 mfd., is bridged across the inductance 36. Variable condensers M and 42, of from 100 to 580 mmf. are respectively bridged across the inductances 35 and 36 for tuning purposes. These padder condensers are adjusted, after the grounding cable has been attached to the bridge circuit and before it is attached to the tank truck in order to balance the bridge circuit.

- The radio frequency voltage of low amplitude may be obtained in any suitable way. For example, it may be produced by a triode 43 which functions as an oscillator. This triode has a plate 44, cathode 45, grid 46 and a heating filament 4'! for the-cathode. The cathode is connected by a wire 48 to negative power wire 25 and by a Wire 49 to one end of the grid coil 50. The other end of the latter is connected by a wire 5|, a resistor 52, of say 50,000 ohms, and a wire 53 to the grid 46. A condenser 54 of say .003 mfd. capacity, is bridged across resistor 52 and a condenser 55, of say .001 mfd. capacity, is bridged across the grid coil 50. The plate 44 is connected by a wire 56 to one end of the feed back coil 51 and the other end of the latter is connected by a wire 58 to the positive power wire 20. A filtering condenser 59, of say 10 mfd. capacity, is bridged across the power wires 20 and 25. The pick up coil 60 of the oscillator is connected by wires GI and 62 to the input terminals 8 and 9, respectively, of the bridge circuit. The grid coil 50, feed back coil 5'! and pick up coil 60 are coupled. These three coils may, for example, be 10 millihenry, powdered-iron-core, radio-frequency chokes. The oscillator described is designed to produce a relatively low voltage, say 6 4 volts, at a frequency of 50,000 cycles per second.

The heating filament 4'! for the cathode 45 of triode 43 and the filament 48 for heating the cathode 6 of triode 4, are connected in. parallel in .a circuit, comprising wires 63 and 64, connected to the secondary 65 of a transformer 56, the primary 61 of which is connected across the power wires I6 and 25. The secondary voltage may, for example, be 6.3 volts.

In practice, all the elements described, with the exception of the grounding cable I3 and its shield 39, are enclosed in an explosion-proof metallic casing, such as shown at 10 in Fig. 2. The power wires for connection to the terminals I4 and I5 and the wires for connection to the terminals II and 12, which as shown in Fig. 1 electrically connect with the switch blade 2 and itscontact 3, respectively, enter the casing 10 through a conduit I3. The shield 33 is connected by a coupling 14 to the casing and thereby grounded. On the outer end of ground wire I3 is a suitable clip I5 for electrical connection to the tank of the tank truck. The casing 10 has a removable cover 16 to enable access to the terminals I4, I5, II and '12 for connection thereto of the wires in conduit 13 and for adjustment of the condensers 4| and 42 and for adjustment of the variable resistor 23 to secure the proper bias for tube 4. The casing 10, with attached ground cable I3 and shield 39 and the various circuits and elements described, can be supplied as one unit to a refinery, for example, for use at a loading station, so that all that has to be done is to connect the terminals I4 and I5 to a suitable power source, the casing 10 to the ground, and the terminals 'II and 12 to whatever device it is desired to operate, such as a signal, audible or visible, as desired. Or a valve in the oil supply line may be opened by electrical means connected to terminals II and 12. In place of the relay, a small neon tube 11 might be used, as shown in Fig. 4, and directly operated by the small current available.

The triodes 4 and 43 may be combined in one tube, such as a 6SN7 or 5692 tube, indicated at 18 in Fig. 3.

The values of resistance, capacity and inductance, given herein, are capable of considerable variation. They are what we consider as optimum values for the purpose and therefore desirable for the practice of the invention in the best way. But they are capable of variation and the invention is not to be limited by the values given.

In use, the ungrounded and grounded sides of the power source are respectively connected to the terminals I4 and I5. This will energize the apparatus. The oscillator produces a radio frequency signal of low amplitude and this is impressed on the input terminals 8 and 9 of the bridge circuit 1. With the impedances of such circuit balanced, no voltage appears at the output terminals I0 and II and the tube 4 is nonconducting because of its negative grid bias. A radio frequency signal is imposed on the grounding cable I3. When the operator attaches the grounding cable I3 by means of clip 15 to the tank truck, the capacity of the tank with reference to the ground becomes electrically connected into the bridge circuit across the inductance 35. This unbalances the bridge circuit.

The amplitude of the radio-frequency signal onthe grounding cable I3 is reduced to a small percentage of its original value and a radio-frequency signal appears at the grid of tube ,4, rendering this tube conducting and thereby enabling the relay l to be energized from its current source. The relay I pulls in to operate the si nal, or other desired device, to show that the rounding cable has been properly connected to the tank of the tank truck. Any static electrical charge will be discharged through the grounding cable l3 and inductance 35 to the ground. In case the relay controls a valve in the oil loadin line, the valve will open when the relay l is energized. Then, should the clip 15 on the grounding cable become detached from the tank truck, the valve will automatically close. Of course, the relay could equally well be arranged to cause the signal to be given when it is deenergized, in which case a signal could be given on detachment of said clip or other failure of the tank grounding means.

The apparatus is designed to fail safely. Failure of the current source, the rectifier, transformer, the oscillator or the electronic tube will prevent the relay from operating.

While the apparatus is designed to respond to the connection into the bridge circuit of the electrostatic capacity of the truck with reference to the ground, it will be clear that it will respond to anything that will unbalance the bridge circuit. This is necessary so long as the tank trucks continue to use grounding chains because the grounding chain of the tank truck may be left down, when the apparatus is connected .to the truck, and form an alternate path to the ground, which in some cases may have substantial resistance and in other cases, substantially none. Thus, the effect of a truck grounding chain that is left down, may be that of a resistor in parallel with inductance 35 or it may act to short circuit said inductance. In either case, the balance of the bridge circuit will be upset and the relay I will operate as described.

Thus, there is provided a safe electrical means for energizing an electrical operator of any suitable or desired kind, when the grounding cable at the tank loading station is electrically connected to the tank of a tank truck to be serviced. The invention is particularly characterized in that the cable used to connect the tank truck to the ground also connects the tank into a balanced bridge circuit and serves as a control means to change the balance in such circuit, and cause a suitable electrical operator to be energized.

What is claimed is:

1. An electronic grounding apparatus for use with tank trucks and the like, comprising, a bridge circuit having four arms with an impedance in each arm, means for impressing on the input terminals of said circuit a radio frequency voltage of low amplitude, a, grounding cable connected at one end to one input terminal of said circuit and adapted for connection at its other end to the tank of the truck, one output terminal of said circuit being grounded, the impedance in that arm of said circuit which extends between the last-named input terminal and the lastnamed output terminal including an inductance coil of low resistance to conduct static charge from said tank through said inductance from said cable to the ground, an electrical operator to be energized when said grounding cable is electrically connected to the tank, an electronic tube controlling said operator, a circuit including said operator and the plate and cathode of said tube and adapted for connection to a source of electricity, a connection from the other output terminal of the bridge circuit to the grid of said tube, said impedances in the bridge circuit being balanced when said cable is not connected to the truck and there being then no voltage at the output terminals of said circuit, said tube being normally nonconducting and rendered conducting when the balance in the bridge circuit is upset by the connection of said cable to the tank truck and the resulting inclusion in said circuit in parallel with said inductance of the capacity between the tank and ground, whereby the operator is energized.

2. An electronic grounding apparatus for use with tank trucks and the like, comprising, a bridge circuit having four arms with an impedance in each arm, means for impressing on the input terminals of said circuit a radio frequency voltage of low amplitude, a grounding cable connected at one end to one input terminal of said circuit and adapted for connection at its other end to the tank of the truck, one output terminal of said circuit being grounded, the impedance in that arm of said circuit which extends between the last-named input terminal and the lastnamed output terminal including an inductance coil of low resistance to conduct static charge from said tank through said inductance from said cable to the ground, a grounded shield for said cable, said cable and shield forming a condenser bridged across said inductance, an electrical operator to be energized when said tank is grounded, an electronic tube controlling said operator, a circuit including said operator and the plate and cathode of said tube and adapted for connection to a source of electricity, a connection from the other output terminal of the bridge circuit to the grid of said tube, said impedances in the bridge circuit being balanced when said cable is not connected to the truck and there being then no voltage between the output terminals of said circuit, said tube being normally non-conducting and rendered conducting when the balance in the bridge circuit is upset by the connection of said cable to the tank truck and the resulting inclusion in said circuit in parallel with said inductance of the capacity between the tank and truck, whereby the operator is energized.

ROY A. RIDDLE. THEODORE J. MESH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,432,669 Kliever Dec. 16, 1947 2,443,125 Weathers June 18, 1948 

